The present invention relates to novel proteins as one of major ingredients crucial for head retention of beer, monoclonal antibodies against said proteins, and an assay for determining foam protein contents in final beer products or beer samples during the brewing process using said monoclonal antibodies. The present invention also relates to a method for determining head retention and head retention stability of beer as well as a method for evaluating raw materials of beer and stabilizers for beer, on the basis of said assay.
Beer is essentially made from malt by saccharifying it into wort, subjecting said wort to primary fermentation with yeast, then sending the resulting green beer to post-fermentation (conditioning) followed by filtration and packaging.
Among the most important qualities of appearance of beer brewed by this process is foam. This property is mainly defined by two aspects, i.e. foaming and head retention.
Head retention has been evaluated on the basis of physicochemical characteristics of foam such as disintegration speed of foam or adhesion to a glass surface. However, foam has complex properties so that sufficient reproducibility or accuracy is unable to be obtained on such a physicochemical basis. Moreover, raw materials of beer such as barley and malt or the stability of long-stored beer for head retention can be evaluated only after the beer has actually been brewed. Therefore, it has been desired to establish a reproducible and rapid evaluation method.
Thus, a method for determining head retention and head retention stability using polyclonal antibodies against raw foam proteins extracted from beer was developed (JPA No. 333223/95). However, this method involved comprehensively testing several foam proteins, and could not detect a minute amount of ingredient-specific foam proteins. Therefore, it has been desired to develop a better method with sufficient sensitivity to detect even a minute amount of ingredient-specific foam proteins.